Pulse stretcher for a receiver of a pneumatic tire low pressure monitoring and warning system

ABSTRACT

An electrical apparatus or pulse stretcher is provided and a pneumatic tire low pressure monitoring and warning system using same wherein such apparatus increases the effective time duration of useable electrical signals supplied thereto to thereby activate an indicator associated therewith. The apparatus comprises an NPN transistor having base, collector, and emitter electrodes and a cooperating PNP transistor having base, collector, and emitter electrodes with the PNP transistor having its collector electrode connected directly to the indicator and to the base of the NPN transistor by a positive feedback loop, each useable signal being supplied to the base of the NPN transistor through a rectifying diode and stored in a capacitor connected functionally from base to ground. The signal operates to turn the PNP transistor ON and simultaneously supply a voltage through the collector electrode of the PNP transistor to activate the indicator whereby the transistors operate to increase the effective time duration of each useable signal supplied to the NPN transistor.

United States Patent Hill [ Mar. 12, 1974 PULSE STRETCHER FOR A RECEIVER OF A PNEUMATIC TIRE LOW PRESSURE MONITORING AND WARNING SYSTEM Inventor:

US. Cl. 340/58, 340/224 Int. Cl. B60c 23/02 Field of Search 340/58, 224; ZOO/61.22,

ZOO/61.25, 61.26

References Cited UNITED STATES PATENTS 9/1972 Strenglein 340/58 6/1971 Koonce 340/58 1 1/1958 Primary ExaminerAlvin H. Waring Attorney, Agent, or F irm-Joseph V. Tassone Strickland et al 340/58 [5 7] ABSTRACT An electrical apparatus or pulse stretcher is provided and a pneumatic tire low pressure monitoring and warning system using same wherein such apparatus increases the effective time duration of useable electrical signals supplied thereto to thereby activate an indicator associated therewith. The apparatus comprises an NPN transistor having base, collector, and emitter electrodes and a cooperating PNP transistor having base, collector, and emitter electrodes with the PNP transistor having its collector electrode connected directly to the indicator and to the base of the NPN transistor by a positive feedback loop, each useable signal being supplied to the base of the NPN transistor through a rectifying diode and stored in a capacitor connected functionally from base to ground. The

signal operates to turn the PNP transistor ON and simultaneously supply a voltage through the collector electrode of the PNP transistor to activate the indicator whereby the transistors operate to increase the effective time duration of each useable signal supplied to the NPN transistor.

5 Claims, 5 Drawing Figures I f SENSOR SENSOR POWER SUPPLY TRANSMITTER TRANSMITTER-\4O 40 W E G 5| RECEIVER RECEIVING REC IVIN ANTENNA ANTENNA 1/ l 7 43 46 RP 43 SUMMER DETECTOR mi 43 43 AMPLlFiER AND R CEIVING RECEIVING l ANTENNA ANTENNA 40 M40 RECTIFIER PULSE sTR TCHER lRANSMlTTER TRANSMITTER INTEGRATOR |ND1CATOR CONTROL E SENSOR SENSOR 57/ 58 INDICATOR PULSE STRETCI-IER FOR A RECEIVER OF A PNEUMATIC TIRE LOW PRESSURE MONITORING AND WARNING SYSTEM BACKGROUND OF THE INVENTION fective width of pulses or time duration of the output signals from the transmitter under conditions where the wheel assembly is rotating is dependent on the rotational velocity of such wheel assembly. It has been found that under conditions where pulses of short widths or of short time duration are provided the overall operation of the system may be unsatisfactory because the indicator will not provide a reliable indication.

SUMMARY This invention provides an electrical apparatus or pulse stretcher and a pneumatic tire low pressure monitoring and warning system using same wherein such apparatus increases the effective time duration of useable electrical signals supplied thereto to thereby reliably activate an indicator associated therewith. The apparatus comprises an NPN transistor having base, collector,

and emitter electrodes and a cooperating PNP transistor having base, collector, and emitter electrodes with the PNP transistor having its collector electrode con nected directly to the indicator and to the base of the NPN transistor by a positive feedback loop, each useable signal being supplied to the base of the NPN transistor through a rectifying diode and stored on a capacitor connected functionally from base to ground. The signal operates to turn the PNP transistor ON and simultaneously supply a voltage through the collector electrode of the PN P transistor to activate the indicator whereby the transistors operate to increase the effective time duration of each useable signal supplied to the NPN transistor.

Other details, uses, and advantages of this invention will be readily apparent from the embodiments thereof presented in the following specification, claims and drawing.

BRIEF DESCRIPTION OF THE DRAWING The accompanying drawing shows a present preferred embodiment of this invention in which FIG. 1 is a perspective view illustrating an exemplary motor vehicle utilizing one embodiment ofa pneumatic tire low pressure monitoring and warning system which employs the improved electrical apparatus of this invention;

FIG. 2 is a schematic presentation of the exemplary system utilized in the vehicle of FIG. 1;

FIG. 2A is a fragmentary view of a typical assembly comprised of a sensor, transmitter, and battery comprising the' system of FIG. 2 with such assembly being mounted on a hub of one of the tires of the vehicle of FIG. 1;

FIG. 2B is a schematic diagram highlighting that each receiving antenna receives a useable signal only during an angular portion of each rotation of its associated transmitter; and

FIG.3 is a schematic electrical diagram of the electrical apparatus of this invention.

DESCRIPTION OF THE OVERALL SYSTEM Reference is now made to FIG. 1 of the drawing which illustratesv a motor vehicle shown in this example of the invention as a four-wheeled passenger automobile 30 of well known construction which has a plurality of four wheel assemblies-32 and each wheel assembly 32 is comprised of a rotatable support in the form of a hub or rim 33 with each hub 33 carrying an associated tubeless tire 34, in a well known manner, which is inflated to a predetermined pressure with a suitable fluid such as ambient air. Each wheel assembly 32 is rotatable about an associated central axis of rotation 35 whereby the associated hub 33 and tire 34 are similarly rotatable about such central axis and in a well known manner. The vehicle 30 is powered by a suitable engine which usually drives two of the wheel assemblies 32, either the front or rear two, and the vehicle 30 utilizes one exemplary embodiment of the pneumatic tire low pressure monitoring and warning system of this invention which is designated generally by the reference numeral 36 and such system serves to warn the operator of the vehicle 30 in the event of an abnormally low fluid pressure, pneumatic pressure in this example, in any one of the four tires 34 and in a manner which will be presented in detail hereinafter.

For convenience and ease of presentation the exemplary system 36 has been illustrated as being used on a vehicle in the form of a passenger-type automobile having a plurality of four tubeless tires each of which is inflated to a predetermined pressure. However, it will be appreciated that the system is fully applicable to all types of vehicles employing either tubeless or tube-type pneumatic tires, or the like, including buses, trucks, trailers, and similar vehicles.

The system 36 comprises a plurality of four sensing means or sensors 37, see FIG. 2, and each sensor 37 is carried by an associated wheel assembly 32 and is preferably suitably installed on the hub 33 of its associated wheel assembly in a fixed manner. The detailed construction and operation of a typical sensor 37 will be presented subsequently.

The system 36 comprises a plurality of transmitters 40, each operatively connected to and'being activated or actuated by an associated sensor 37 and in this example the sensor 37 and transmitter 40 associating with a particular wheel assembly 32 is provided with a selfcontained power source in the form of a battery 41 and the sensor 37, transmitter 40, and battery 41 of each particular wheel assembly is provided as a single unit or assembly which is designated generally by the reference numeral 42, see FIG. 2A. The assembly 42 may be suitably installed within its associated hub 33 by threaded bolt, welding, or the like, and as a practical matter the assembly 42 and hence its transmitter 40 is located at a position which is radially displaced by adistance D from the central axis of rotation 35 of its wheel assembly 32, see FIGS. 1 and 2A.

The sensor 37 is comprised of a sealed pressurized hemispherical dome which dimples in a substantial predetermined manner when it is exposed to an external pressure greater than a predetermined minimum. The dimple action serves as a normally open electrical snap switch which closes by oil can action whenever the external pneumatic pressure falls below the predetermined minimum pressure which in reality is the minimum air pressure required to assure satisfactory operation of the associated tire 34. Y

The transmitter 40, which will also be referred to as oscillator 40, is actuated by the snap action of its sensor 37 whereby the associated battery 41 provides electricalpower for the oscillator 40. The oscillator 40 is a self-pulsed oscillator whichgeneratesa radio frequency (RF) signal with distinct, readily identifiable characteristics to eliminate false alarms. The oscillator utilizes a tank circuit having a coil which is unshielded and unobstructed to the greatest extent possible to establish an external magnetic alternating near field and thereby use such coil as the transmitting antenna. Each transmitter 40 operatively associates with an associated one of four fixed receiving antennas 43 comprising the system 36 and the antennas 43 will be described in detail subsequently.

' For certain applications where it may be desired to take advantage of the minimal licensing requirements in the so-called citizens band of radio frequencies ranging between 26.97 27.27 megahertz (Mhz), the oscillator frequency may be located within this band and the transmitter 40 then uitlizes near field transmission. The median frequency in this band is 27.12 Mhz which corresponds to a wave length of 36.26 feet and such distance is considerably greater than the distance required for the system 36 of this invention to span from a hub 33 of any particular wheel assembly 32 of a vehicle using system 36 to a location on such vehicle where an antenna for the system is likely to be located.

The use of near field transmission has the distinct advantages that in the near field zone the stationary field is of greater magnitude than the traveling field, and attenuation of the stationary field perunit of distance is greater than that for the traveling field whereby interference with adjacent electrical apparatus as well as electrical apparatus of the vehicle is minimized. F urther, because transmission basically may be considered as the coupling between a stationary coil on a receiving antenna 43 and a rotating coil of an associated transmitter 40, such transmission will be controlled by the coupling factor whereby maximum magnetic coupling will provide maximum transmission.

Because of practical considerations of economy and simplicity in detecting a low pressure condition in a rotating pressurized tire, each transmitter assembly 42 and its transmitter 40 is preferably located off center, as indicated earlier, by the distance D from the central axis of rotation of its associated wheel assembly 32 and hub 33. However, the assembly 42 is of small weight (roughly an ounce) and the weight thereof may be easily balanced by a regular small size automobile tire balancing weight, if desired.

With off center mounting, the previously mentioned coupling factor between a rotating transmitter and the fixed coil of its receiving antenna 43 varies considerably as each wheel assembly rotates because of thein shielding interposed between the coils at different relative positions thereof. As a result of these factors the transmitted output signal from the transmitter 40 is of sufficient strength to be useable only during a portion of each revolution or rotation of its wheel assembly 32. Stated in another manner, because each receiving antenna 43 is attached at a fixed position on the vehicle adjacent its wheel assembly 32, the antenna 43 receives a useable output signal from the transmitteronly during a portion of each complete rotation of the transmitter therepast. However, since it is known that the magnetic near field varies inversely as the third power of distance, then the received signal during part of the rotation will be substantially stronger than the received signal would be if a more constant transmission distance was selected. The system 36 utilizes a receiver 45 which is operatively connected to each receiving antenna 43 by an associated coaxial cable 46 and the receiver employs unique means for increasing the effective time duration of the useable portions of the output signals from the transmitter 40 to activate or otherwise energize an associated indicator 47 comprising system 36 and such indicator is operatively connected to the receiver 45 in a manner to be described.

The indicator 47 may be of any suitable type. For example, such indicator may be in the form of a light which is observed visually or such indicator may be in the form of an audible indicator such as a bell or buzzer.

The system 36 in addition to the batteries 41 comprising assemblies 42, also has a power source for its receiver 45 and such power source is designated generally by the referencenumeral 50 and is suitably operatively connected to the receiver 45 as illustrated at 51. The power source 50 may comprise any suitable source of power and in this example is the usual battery provided for the vehicle 30.

Each'transmitter 40 is energized by a low pressure indication as determined by its sensor 37 and will provide continuous pulsed output signals. In general, only during certain time intervals associated ones of these signals are of sufficient strength that they are readily received by an associated receiving antenna'43 and as will now be explained particularly in connection with FIGS. 1 and 2B. 7

Under conditions wherein the vehicle 30 is standing still, the signal from a transmitter 40 is processed through the receiver 45 and may activate the indicator 47, such as an indicator lamp 47, so that the lamp 47 is ON or OFF depending upon the relative location of the transmitter 40 and receiving antenna 43. In those instances when the vehicle 30 is moving at a relatively low speed, the indicator lamp 47 will be turned ON and OFF sequentially; however, it has been found that the lamp 47, in this case, is turned ON for a sufficiently long time interval to assure full brightness and, conversely, when such lamp is turned OFF it is extinguished completely. With the vehicle moving at such slow speeds, the pulse of light will therefore be fully visible and the low pulse repetition rate will result in a flickering action by the lamp 47. IF the vehicle 30 is moving at higher speeds the lamp 47 may be turned ON for a time period which is insufficient to insure full brightness. This performance of the lamp at higher vehicle speeds in combination with the higher pulse repetition rate due to faster rotation reduces the flickering;

however, the total perceptible light may be inadequate to be used as an indicator.

To highlight this situation reference is made to FIG. 2B of the drawings wherein it is seen that for each full rotation of a wheel the transmission level is high enough to activate or light the indicator lamp 47 for X degrees while such lamp is dark for the remaining (360X) degrees. By way of an example, X may be 30, in which case the indicator lamp will be dark for a period roughly 11 times as long as the lighted period. Thus, it can be readily seen that an operating transmitter 40 used in a pneumatic tire of a given size will generate a signal having a particular pulse frequency determined by the emission characteristics of the transmitter and the speed of'the vehicle. It is also apparent that the performance of the indicator 47 may be substantially improved if the indicator ON time or the time that it is activated is increased relative to its OFF time. In particular, the performance of the indicator 47 may be substantially improved if the effective time duration of a useable signal received by each receiving antenna 43 is increased and this may be achieved by a technique referred to popularly as pulse stretching and means for achieving such pulse stretching is provided in the receiver 45.

The receiver 45 minimizes false alarms by rejecting potentially false alarm inputs including; power supply disturbances generated by the electrical equipment of the vehicle 30, including the starter, horn, window washer, windshield wipers, key alarms, etc.; RF signals generated by natural atmospheric electrical disturbances such as static; RF signals generated by the above-mentioned electrical equipment of the vehicle 30; RF signals generated by electrical equipment external to the vehicle; voice-modulated as well as continuous-wave signals within the selected RF transmission band; and modulated as well as continuous-wave RF signals outside the selected band. Conversely, the RF receiver 45 very reliably recognizes and activates the indicator 47 when receiving a pneumatic tire low pressure warning signal in the form of an RF signal having all of the following characteristics of being in the selected RF band, being an RF signal which is pulsating at the predetermined frequency defined by the selfpulsed oscillator, and being an RF signal which is pulsating at a rate and with a pulse width determined by the angle X of rotation over which a recognizable signal is received in combination with the rotational velocity of an associated wheel assembly 32 of the vehicle 30.

The receiver 45 has an RF pass band which is reduced to a minimum compatible with assured inclusion of the selected RF band under all environmental conditions and has means minimizing or eliminating the above-mentioned false alarm inputs while assuring recognition of a signal indicating a low tire pressure and as will be apparent from the following description. In

particular. the receiver 45 has a summer 53 which receives RF signals from an RF transmission line 46 in the event of a low pressure condition in a vehicle tire associated therewith and such signals are then fed to an RF amplifier 54. The amplifier 54 employs a plurality of two transformer coupled stages having tuned primaries and untuned secondaries to amplify the RF signal whereby RF amplification is held at a minimum in view of its relatively. high cost and regeneration problems usually associated therewith. The signals from the RF amplifier 54 are fed to a diode amplitude detector 55 which is forward biased to facilitate its ability to perform at very low signal levels and the detector 55 is followed by a low frequency (LF) amplifier, limiter, and filter circuit 56 which serves to attenuate undesired signals. The circuit 56 is a combination LF limiter/band pass amplifier which prevents LF signals on frequencies outside the predetermined frequency band of the oscillator from reaching a level which may activate the indicator. The circuit 56 is followed by a rectifierintegrator circuit 57 which integrates the LF pulses in the pulse train. This circuitry will insure that a pulse train rather than noise spikes is required to activate the indicator while the shortest authentic pulse train will suffice to let the rectified voltage reach a level which will activate succeeding or downstream circuits in the receiver. The circuit 57 thus serves to eliminate the effect of noise spikes and provides more reliable operation the longer the required integration time can be made. The circuit 57 is followed by a pulse stretcher and indicator control circuit 58 and this circuit is particularly useful in overcoming the effect of short trains of pulses. The circuit 58 serves as means for increasing the effective time duration of useable ones of the output signals provided to RF receiver 45 by receiving antennas 43 and insures that a satisfactory indicator sig-- nal is provided to the indicator 47 to present a distinct indication. The pulse stretcher 58 is inherently a regenerative device whereby it also increases the sensitivity of the RF receiver since any signal which is capable of activating the pulse stretcher will provide a saturated output signal. The circuit 58 activates indicator 47 to warn the operator of the vehicle 30 in the event of a.

low pressure condition in any one of the vehicle tires. The receiver 45 also has suitable means in its power supply 50 for filtering such power supply to reduce power supply line disturbances to a tolerable level.

Having described the general operation of the svstem 36 in connection with the exemplary vehicle 30, a detailed description will now be presented of the improved apparatus of this invention which may be used substantially interchangeably with the circuit 58 previously described in a general manner in the operation of the overall system and such apparatus is popularly referred to as a pulse stretcher and indicator control circuit which is designated by the reference numeral 58A.

Pulse Stretcher and Indicator Control 58A The pulse stretcher and indicator control apparatus or circuit 58A (see FIG. 3) provides stretching of each incoming pulse or signal from the transmitter by utilizing an amplifier in the form of an NPN transistor 204A having the usual base, collector, and emitter electrodes and a cooperating PNP transistor 205A also having base, collector, and emitter electrodes. A positive input signal will charge a comparatively large capacitor(not shown) of the rectifier-integrator circuit through a rec,- tifying diode (not shown) to a positive level which will suffice to turn transistor 204A ON and lower its collector voltage to the value approaching ground potential thereby turning transistor 205A ON and supplying substantially full B+ voltage upwards of plus 15 volts through lead 206A which is supplied to one terminal of the indicator 47 of receiver 45 while the other terminal 47 is connected to ground. The transistor 205A will remain ON until the charge on the storage capacitor has diminished to an extent where the voltage across the capacitor is insufficient to maintain transistor 204A in an ON condition. Y

The circuit 58A also has a positive feedback circuit or loop 209A operatively connected between the collector of transistor 205A and the base of transistor 204A and such loop 209A includes a resistor 207A. However, assume that resistor 207A is eliminated, the circuitry will in essence be a two stage amplifier and its turn OFF will be determined by the time constant established-by the previously mentioned capacitor of the rectifier-integrator circuit and its associated resistive circuitry which may be of the order of approximately 100 milliseconds. By adding the resistor 207A the circuit 58A operates as an undercompensated switching amplifier, i.e., feedback current through the resistor 207A by itself is insufficient to maintain the associated v indicator of receiver 45 in an ON condition and it must therefore be supplemented with input pulses.

in this example of receiver 45 the indicator 47 is in the form of a lamp and as the voltage across the lamp increases, the positive feedback through the resistor 207A adds to the input signal and provides a switching action. This will serve to turn the indicator lamp 47 fully ON even if the input signal is insufficient to accomplish this. Additionally, the positive feedback generates a hysteresis effect on the input switching levels since it takes less input signalto hold the lamp ON than it does to turn it ON initially. Thus, it is seen that the incoming pulse is stretched for three reasons, hysteresis effect due to positive feedback through loop 209A, time delay in base voltage leak-off or reduction in potential of said base of transistor 205A, and an additional time delay in leak-off resulting from positive feedback through loop 209A whereby the overall effect is to increase the time delay to approximately 150 milliseconds. The circuit 58A is connected to the indicator 47 by the lead 206A previously mentioned and power for circuit 58A is supplied by a lead 208A.

While present exemplary embodiments of this invention, and methods of practicing the same, have been illustrated and described, it will be recognized that this invention may be otherwise variously embodied and 8 sure condition in a pneumatic tire supported on an associated vehicle by a rotatable support, a transmitter carried by and being rotatable with said rotatable support with said transmitter being actuated by said sensing means and providing output signals'at a radio frequency in response to said low pressure condition; a receiving antenna attached at a fixed position on said vehicle adjacent said tire; said antenna receiving useable ones of said output signals only during a portion of each complete rotation of said transmitter therepast; a receiver; means operatively connecting said receiving antenna to said receiver; indicating means operatively connected to said receiver and being activated thereby; and means insaid receiver for increasing the effective time duration of said useable ones of said output signals, said increasing means assuring said indicating means is activated only in response to said low pressure condition and comprising, an NPN transistor having base, collector, and emitter electrodes, a cooperating PNP transistor having base, collector, and emitter electrodes, said PNP transistor having its collector electrode connected to said indicating means and a positive I feedback circuit connecting said collector electrode of saidPNP transistor to said base electrode of said NPN transistor, each useable signal being supplied to said base of said NPN transistor and operating to turn said PN P transistor ON and simultaneously supply a voltage through said collector electrode of said PNP transistor to activate said indicating means, each useable signal being increased ineffective time duration due to hysteresis of said feedback circuit, time delay in reduction in potential of said base of said PNP transistor, and time delay introduced by said feedback circuit.

2. A system asset forth in claim 1 in which said indicating means is an indicator lamp.

3. A system as set forth in claim 1 in which said transmitter is a self-pulsed transmitter, and said indicating means is an indicator lamp.

4. A system as set forth in claim 3 in which said positive feedback circuit hasa-resistor provided therein.

, 5,.-A system as set forth in claim 4 and further comprising a second resistor operatively connected between said collector electrode of said PNP transistor and said base electrodeof said PNPtransistor. 

1. A pneumatic tire low pressure monitoring and warning system comprising, means sensing a low pressure condition in a pneumatic tire supported on an associated vehicle by a rotatable support, a transmitter carried by and being rotatable with said rotatable support with said transmitter being actuated by said sensing means and providing output signals at a radio frequency in response to said low pressure condition; a receiving antenna attached at a fixed position on said vehicle adjacent said tire; said antenna receiving useable ones of said output signals only during a portion of each complete rotation of said transmitter therepast; a receiver; means operatively connecting said receiving antenna to said receiver; indicating means operatively connected to said receiver and being activated thereby; and means in said receiver for increasing the effective time duration of said useable ones of said output signals, said increasing means assuring said indicating means is activated only in response to said low pressure condition and comprising, an NPN transistor having base, collector, and emitter electrodes, a cooperating PNP transistor having base, collector, and emitter electrodes, said PNP transistor having its collector electrode connected to said indicating means and a positive feedback circuit connecting said collector electrode of said PNP transistor to said base electrode of said NPN transistor, each useable signal being supplied to said base of said NPN transistor and operating to turn said PNP transistor ON and simultaneously supply a voltage through said collector electrode of said PNP transistor to activate said indicating means, each useable signal being increased in effective time duration due to hysteresis of said feedback circuit, time delay in reduction in potential of said base of said PNP transistor, and time delay introduced by said feedback circuit.
 2. A system as set forth in claim 1 in which said indicating means is an indicator lamp.
 3. A system as set forth in claim 1 in which said transmitter is a self-pulsed transmitter, and said indicating means is an indicator lamp.
 4. A system as set forth in claim 3 in which said positive feedback circuit has a resistor provided therein.
 5. A system as set forth in claim 4 and further comprising a second resistor operatively connected between said collector electrode of said PNP transistor and said base electrode of said PNP transistor. 